One known example of a wave gear device is what is known as a silk-hat-type device, such as is disclosed in Patent Document 1. In this type of wave gear device, a hollow part having a large inside diameter passing through the device along the center axis line is readily formed in the center of the device, and the hollow part can be used as space for wiring or the like.
In a silk-hat-type wave gear device, a flexible externally toothed gear disposed on the inside of a rigid internally toothed gear has a silk hat shape. The flexible externally toothed gear comprises a cylindrical barrel part capable of flexing in the radial direction, a diaphragm extending outward in the radial direction from one end of the barrel part, and a thick annular boss formed as a continuation of the external peripheral edge of the diaphragm. The region on the side of the open edge, which is the side opposite the diaphragm in the cylindrical barrel part, is an external-tooth-formation portion, where external teeth are formed in the external peripheral surface.
The flexible externally toothed gear is made to flex into an ellipsoidal shape by an ellipsoidally contoured wave generator mounted to the inside of the external-tooth-formation portion, and the flexible externally toothed gear is partially meshed with the rigid internally toothed gear. When the wave generator is rotated, the meshing positions of the two gears move in the circumferential direction, and relative rotation occurs between the two gears, the rotation corresponding to the difference in the number of teeth between the two gears. One gear is fixed in place so as to not rotate, whereby reduced rotation is outputted from the other gear. The wave generator is configured from an annular rigid cam plate, and a wave bearing mounted to the ellipsoidally contoured external peripheral surface of the cam plate. In the silk-hat-type wave gear device, the inside diameter of the hollow part of the wave gear device is stipulated by the inside diameter of a hollow hole in the wave generator, i.e. a hollow hole formed in the cam plate.
Another known example of a wave gear device is what is referred to as a cup-type device such as is disclosed in Patent Document 2. In this type of wave gear device, a flexible externally toothed gear disposed on the inside of a rigid internally toothed gear has a cup shape. The flexible externally toothed gear comprises a cylindrical barrel part capable of flexing in the radial direction, a diaphragm extending inward in the radial direction from one end of the barrel part, and a thick annular or discoid boss formed as a continuation of the internal peripheral edge of the diaphragm. The region on the side of the open edge, which is the side opposite the diaphragm in the cylindrical barrel part, is an external-tooth-formation portion, where external teeth are formed in the external peripheral surface.
The flexible externally toothed gear is made to flex into an ellipsoidal shape by an ellipsoidally contoured wave generator mounted to the inside of the external-tooth-formation portion, and the flexible externally toothed gear is partially meshed with the rigid internally toothed gear. When the wave generator is rotated, the meshing positions of the two gears move in the circumferential direction, and relative rotation occurs between the two gears, the rotation corresponding to the difference in the number of teeth between the two gears. One gear is fixed in place so as to not rotate, whereby reduced rotation is outputted from the other gear. One gear is fixed in place so as to not rotate, whereby reduced rotation is outputted from the other gear. The wave generator is configured from an annular rigid cam plate, a wave bearing mounted to the ellipsoidally contoured external peripheral surface of the cam plate.
Yet another known example of a wave gear device is what is referred to as a flat-type device such as is disclosed in Patent Document 3. In this type of wave gear device, a flexible externally toothed gear disposed on the inside of a rigid internally toothed gear has a simple shape comprising a cylindrical barrel part capable of flexing in the radial direction, and external teeth formed on the circular external peripheral surface of the cylindrical barrel part.
Two rigid internally toothed gears are disposed in parallel on the outer side of the flexible externally toothed gear. The flexible externally toothed gear is made to flex into an ellipsoidal shape by the ellipsoidally contoured wave generator mounted to the inner side of the flexible externally toothed gear, and the flexible externally toothed gear is partially meshed with the rigid internally toothed gears. When the wave generator is rotated, the meshing positions of the flexible externally toothed gear and the two rigid internally toothed gears move in the circumferential direction. One rigid internally toothed gear has the same number of teeth as the flexible externally toothed gear, and the other rigid internally toothed gear has more teeth than the flexible externally toothed gear. Therefore, the flexible externally toothed gear rotates integrally with the rigid internally toothed gear that has the same number of teeth, and relative rotation occurs with the rigid internally toothed gear that has a different number of teeth, the rotation corresponding to the difference in the number of teeth between the two gears. One rigid internally toothed gear is fixed in place so as to not rotate, whereby reduced rotation is outputted from the other rigid internally toothed gear. The wave generator is configured from an annular rigid cam plate, and a wave bearing mounted to the ellipsoidally contoured external peripheral surface of the cam plate.